1. Field of the Invention
The present invention relates to a light measuring device for a single lens reflex camera, and more particularly relates to such a light measuring device which measures light passing through the camera objective lens, both for the exposure determination, i.e. the determination of shutter speed and/or diaphragm aperture and for the detection of the focusing condition.
2. Description of the Prior Art
In the field of the single lens reflex camera, there have been proposed various cameras which measure light for both the exposure determination and the detection of focusing condition. For the light measurement for the exposure time, various types are available, such as a spot light measuring device which measures the light coming from a comparatively narrow area nearby the optical axis of the camera objective lens. Another type is an average or integral light measuring device which measures the light from almost the entire portion of the scene to be photographed.
On the other hand, for the detection of off focusing condition, a device has been known which, as disclosed in Japanese laid-open patent application SHO No. 52-95221, employs a pair of light receiving or photosensor arrays, each array having a plurality of light detecting elements arranged in a line. The device is arranged such that the two photosensor arrays look through different regions of the exit pupil of an objective lens at an object on the optical axis of the objective lens.
It should be recognized here that the spot light measuring device measures the intensity of the light coming from a narrow area of the object on the optical axis of the objective lens, while the focus detecting device detects the focusing condition in a comparatively narrow portion of the object image on the optical axis on a given image forming or focal plane. Thus, both devices measure relatively narrow areas of the object on the optical axis but it is difficult for them to commonly use the same light receiving means because they measure different subjects, i.e. one measures the intensity of light while the other measures focusing condition.
Accordingly, to enable both the spot light measuring and the focus detection, it is necessary to provide two photosensor arrays for the focus detection and a light receiving element for the light measurement for exposure determination. However, there has not been proposed any such combination of the photosensor arrays and a spot light measuring device nor any optical system for introducing light to them.